SV-POW! … All sauropod vertebrae, except when we're talking about Open Access

Things to Make and Do, part 5: anaglyphs (red-and-cyan 3D images)

January 31, 2010

I hope you have a pair of 3D glasses. If you do, then check this baby out:

Brachiosauridae incertae sedis NHM R5937, "The Archbishop", damaged cervical vertebra S in right posterolateral view; red-cyan 3D anaglyph. This image and others of the same specimen copyright the NHM since it's their specimen.

I’ve started to get into the habit recently of photographing some specimens from two slightly different angles: I couldn’t tell you exactly how much rotation I use, but I would guess it’s something like three to five degrees. That’s because I’ve found that flipping back and forth between the two images can give a useful sense of depth. If you don’t believe me, here are two not-quite-identical photos of the Archbishop’s Cervical S: open each of them in a tab, then flick back and forth between them:

Cervical S, first image

Cervical S, second image

It had occurred to me a while back that, just for fun, it would be interesting to composite them into a red-cyan 3D image. But I was prodded into action by two things. First, the free Lego marketing magazine that my boys get sent every month arrived, and with it a freebie pair of cheap cardboard red-cyan glasses. And second, Matt published a steropair of moon images on his blog. Matt’s friend Jarrod is a professional digital effects artist — in fact he’s won Emmies for stuff like blowing up Los Angeles for 24 — and threw together an anaglyph from the moon pictures. I got instructions from Jarrod on how to do this, and was gratified how easy it was. Here you go:

Open the two photos as two layers of a single image.

Using the Colour Levels dialogue, turn the red channel of one of the photos all the way down to zero (so that it appears in shades of cyan)

Using the same dialogue, turn both the blue and green channels of the other photo down to zero (so that it appears in shades of red)

Change the Layer Mode of the top layer to Brighten Only

That’s it, you’re done! Save the resulting composite image as a JPEG and upload it to your sauropod-vertebra blog. Jarrod uses PhotoShop; I use the Gimp, which is a free more-or-less equivalent program — the same technique works fine with both.

If I was pleasantly surprised at how simple the technique is, I was astounded at the quality of the result. I’d expected all the colour of the image to be gone, and to see a vague monochrome haze. Instead, I saw rock-solid 3D in full colour — truly informative images that convey the morphology of complex bones far better than any published figure I’ve ever seen. Seriously, go get your red-cyan glasses, you won’t regret it.

Here is another anaglyph of the same vertebra, in posterior view close-up, showing in detail what looks suspiciously like a hyposphene below and between the postzygs. (If this is indeed a hypophene, then I believe it’s unique among sauropods.)

Cervical S, posterior view in close-up, showing possible hyposphene.

Journals have occasionally published stereopair images of palaeo specimens: small images a couple of inches wide, next to each other, which you can supposedly see as a single 3D image if you cross your eyes in just the right light provided the wind is from the southeast — personally, I have never been able to see these things, thought Matt can. But these big, full-colour 3d images are orders of magnitude more information.

I’ve never seen one in a journal, in part of course because colour printing is such an insanely expensive luxury. But as Matt says, we all live in the future now, and I hope that’s about to change. I will be sending the Archbishop description, when it’s done, to PLoS ONE, which because of its electronic-only format can include any number of full-colour figures at no cost. I plan to send a few anaglyphs among the more conventional figures. Fingers crossed that they make it into the published version — I guess if I get a traditionalist reviewer, he might think these are frivolous and demand that I remove them. But they are not frivolous: they may be the most informative figures I have ever prepared.

Let me take this opportunity to dispell the myth that stereopairs are supposed to be visible with the naked eye. Yes, some of us are lucky enough to view stereopairs by crossing our eyes, but that is not how its supposed to work. Instead, regarless of eye-crossing ability, stereopairs are correctly viewed with a stereoscopic viewer – which looks like glasses on a metal stand (see examples here http://www.fullam.com/Semacces.htm).

On another on note – does anyone know if the ideal difference in angle between two images used for an anaglyph is the same as for two images used in a stereopair? If so, there are plenty of web-pages out there that tell you how to calculate the angle for a stereopair.

Well, there is an advantage to those of use who *can* cross their eyes :) I do still see one advantage of stereopairs – that they’re still easy to look at without the equipment. That is, we can all get plenty of clear info out of stereopairs even viewing them in 2D, whereas anaglyphs are alot less clear without the glasses. I think thats probably why (beyond the lack of need for color) why scientific pubs have generally gone for stereopairs, because a single stereopair image is still a perfectly good specimen image for the naked eye.

I hasten to add that, in fact, stereo pairs that are not too big — i.e., the centers are no farther apart than one’s eyes — are easy to see in 3D without any equipment, and are enormously appreciated by those who have learned how. It’s not at all difficult to learn how; it, like so much else, just takes a little practice.

However, the correct technique is not to cross your eyes. That does work if you swap the images left-for-right; otherwise it looks turned inside-out, like looking at the image printed inside a hollow mold of the object. (Swapping images and looking cross-eyed, which does work, is more fatiguing than the correct method.) Instead, simply look off into the distance just above the images, and jump your gaze down to the image pair. They will be mostly merged, and it’s easy then to get them to merge precisely, but (probably) out of focus. After that, it just takes some exercise and practice to get them to come into focus. Once the technique is learned, it’s never lost, and you have a new skill.

I can’t do the parallel view method that Nathan describes, and i’ve practiced for literally hours – but crossviewing (or the crosseyed method) only took me a few minutes. I can give anecdotal evidence that on the internet there are far more examples of images set up for crossviewing than there are for parallel – which seems to indicate the crossviewing method is easier to learn. And i beg to differ, Nathan, but i experience NO fatigue from crossviewing, so i’m not sure why are you claiming that parallel is “less” fatiguing. it’s a matter of personal preference, not really ‘right vs. wrong’.

either method is far superior to anaglyph, because of the loss of color data inherent in anaglyphs. anaglyph is dead tech, at this point. the new school are either polarized light lenses (what you saw Avatar with at a non-Imax movie theater) or LCD shutter glasses (at some IMAX screens, these are the bulkier glasses). polarized lenses lose brightness, shutters give you full brightness. but polarized are far cheaper and reliable. neither of these glasses are feasible for web – current computer monitors can’t polarize two images nor flicker them fast enough.

so please post lots more stereoscopic images, and use crossview as the default! that’s my vote, anyways. or you could go full out and embed a flash player that will allow the user to choose their preferred method – these guys have one that’s kinda overkill, but it should give you an idea of the possibilities.

“either method is far superior to anaglyph, because of the loss of color data inherent in anaglyphs. anaglyph is dead tech, at this point.”

You are mistaken. The thing that impressed me the most about the images in this post is how well they preserve the colour of the specimens.

No doubt polarised or shuttered lenses would be yet better, but as you pointed out they are not possible in most cases. Red/green glasses, on the other hand, cost 40 cents per pair, have no moving parts and never break down.

blue: I don’t know how you can compare the two techniques if you have only done one. I do both, and notice a distinct difference. With the number of images found in this posting, it doesn’t matter, but if I were, e.g., exploring Mars that way (http://roadtoendeavour.wordpress.com/) all day long, it would. It’s nothing exotic; it’s the same fatigue as reading ingredients lists at the supermarket, or extracting gonads of fruit flies.

I think I deserve credit for the original request to our esteemed proprietor to post stereo pairs … here, one year gone: /2009/02/17/xenoposeidon-week-day-8-somewhat-belatedly-those-wrinkles/#comment-2228 — “How about a low-tech stereoscopic image pair, i.e. two shots with the camera moved a little between shots? Why isn’t this a standard part of paleo presentations?“

[…] the stereo information in these pairs of photos that Jeff took? My favourite way is using red-cyan anaglyphs — those goofy 3d images that you look at through 3d glasses. To compare, I did this to […]

[…] I hope that’s clear. What I really should have done, of course, was take my own good advice and get photos from every angle — and, ideally, pairs that would have allowed me to show the relevant features as anaglyphs. […]

[…] taken from somewhat different angles, I thought I’d have a go at compositing them into a red-cyan anaglyph. Because the variation in camera position is mostly dorsoventral rather than anteroposterior, the […]